Conventional die-level packaged microelectronic devices typically include a microelectronic die, an interposer substrate or lead frame attached to the die, and a moulded casing around the die. The die generally includes an integrated circuit coupled to a plurality of bond-pads. The bond-pads are typically coupled to contacts on the interposer substrate or lead frame, and serve as external electrical contacts through which supply voltage, signals, etc., are transmitted to and from the integrated circuit. In addition to contacts, interposer substrates can also include ball-pads coupled to the contacts by conductive traces supported in a dielectric material. Solder balls can be attached to the ball-pads in one-to-one correspondence to define a “ball-grid array.” Packaged microelectronic devices with ball-grid arrays are generally higher grade packages that have lower profiles and higher pin counts than conventional packages using lead frames.
One process for making a packaged microelectronic device with a ball-grid array includes (a) forming a plurality of dies on a semiconductor wafer, (b) cutting the wafer to separate or singulate the dies, (c) attaching individual dies to an interposer substrate, (d) wire-bonding bond-pads on the dies to contacts on the interposer substrate, and (e) encapsulating the dies with a suitable moulding compound. Packaged microelectronic devices made in the foregoing manner are often used in cellphones, pagers, personal digital assistants, computers, and other electronic products. As the demand for these products grows, there is a continuing drive to increase the performance of packaged microelectronic devices while at the same time reducing the height and surface area or “footprint” of such devices on printed circuit boards. Reducing the size of microelectronic devices, however, becomes more difficult as the performance increases because higher performance typically requires more integrated circuitry and bond-pads.
FIG. 1 is a partially cut-way isometric view of a packaged microelectronic device 100 configured in accordance with the prior art. The packaged microelectronic device 100 includes a microelectronic die 110 attached to an interconnecting substrate 120 in a conventional board-on-chip (BOC) arrangement. The microelectronic die 110 includes an integrated circuit 116 electrically coupled to a plurality of terminals (e.g., bond-pads) 112. Each of the terminals 112 is electrically coupled to a corresponding bond-finger or contact 122 on the interconnecting substrate 120 by an individual wire-bond 114. Each of the contacts 122 is in turn electrically connected to a corresponding ball-pad 126 by a conductive line or trace 124 formed on the surface of the substrate 120. After the electrical connections have been made, the microelectronic die 110 can be encapsulated with a suitable mold compound 140 for protection. Solder balls (not shown) can be attached to the ball-pads 126 in one-to-one correspondence to form a ball-grid array for attaching the packaged microelectronic device 100 to a printed circuit board (PCB), printed wiring assembly (PWA), and/or other electronic interfaces (not shown).
As the performance of the microelectronic die 110 increases, the number of terminals 112 also increases. Combining this with the trend to make the die 110 smaller results in a very fine-pitch array of terminals 112 on the die 110. Providing enough contacts 122 and traces 124 to accommodate the terminals 112 causes the surface of the interconnecting substrate 112 to become very congested near the die 110. At some point, the surface of the substrate 120 will become so congested that it will no longer be possible to add any additional contacts or traces. This constraint limits the ability to shrink the microelectronic device 100 further, especially if the performance of the die 110 increases.
FIG. 2 is a partially cut-away isometric view of another packaged microelectronic device 200 configured in accordance with the prior art. The packaged microelectronic device 200 includes a microelectronic die 210 bonded to an interconnecting substrate 220 in a conventional chip-on-board (COB) arrangement. The microelectronic die 210 includes an integrated circuit 216 electrically coupled to a plurality of first terminals 212a and a plurality of second terminals 212b . As shown, the first terminals 212a are arranged along one side of the die 210 and the second terminals 212b are arranged along the other side of the die 210. Each of the terminals 212 is electrically connected to a corresponding contact 222 on the interconnecting substrate 220 by an individual wire-bond 214. Each of the contacts 222 is in turn electrically coupled to a corresponding ball-pad 226 by a conductive line 224. In the conventional COB arrangement illustrated in FIG. 2, the ball-pads 226 are located on a back surface of the interconnecting substrate 220, and a portion of each conductive line 224 extends through the substrate 220 to reach the corresponding ball-pad 226. After all the electrical connections have been made, the microelectronic 210 is encased in a suitable mold compound 240.
Many of the congestion problems discussed above with reference to FIG. 1 also apply to the packaged microelectronic device 200 illustrated in FIG. 2. For example, as the performance of the microelectronic die 210 increases, the number of terminals 212 and other die components also increases. As a result, the common way to reduce the overall size of the packaged device 200 is to reduce the size of the interconnecting substrate 220. As the interconnecting substrate 220 becomes smaller, however, the contacts 222 need to be smaller and more compressed because the area to accommodate them is reduced. This makes attachment of the wire-bonds 214 to the contacts 222 increasingly difficult which, in turn, tends to limit the ability to shrink the overall package further.